Features of the relaxor state in the simple-perovskite mixed-oxide system (1 - x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃

The mixed-oxide system (1 - x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) has a simple perovskite structure and exhibits relaxor behavior for 0 ≤ x ≤ 0.30 (low Ti contents). To understand the relaxor state in PMN-xPT, the crystallographic features of the ferroelectric states were investigated via transmission electron microscopy, taking advantage of Friedel's law failure. Polar regions having '110'_C and '001'_C components were observed separately both below and near T_m, the maximum temperature of the dielectric permittivity for the relaxor. As a result, the relaxor state for 0 < x ≤ 0.30 was identified as an assembly of nanometer-scale polar domains with rhombohedral symmetry. On the other hand, the ferroelectric states for 0.40 ≤ x ≤ 0.70 are characterized by a ferroelectric M_C-type monoclinic state, having a polarization vector in the {100}_C planes. Thus, the FR/FM_C boundary around x = 0.35 was identified as the morphotropic phase boundary (MPB), nearly parallel to the temperature axis.